"Why? Because it lends a whole political atmosphere to whatever he's going to be saying to the Congress."

By the end of June, Francis is to release an encyclical — a teaching document — warning about the dangers of climate change and how mankind must pay attention. The Pontiff is also expected to bring up the issue when he addresses Congress in September.

"There's no way the Pope is going to come out of that chamber without people putting a political spin on it whether to the right or the left," Sirico said.

"The Pope is visiting us not as the head of Vatican City State, not as a politician, not as a monarch, but as a pastor, as a bishop."

Sirico's group is a non-profit research organization "dedicated to the study of free-market economics informed by religious faith and moral absolutes."